Recurring Ice Dams on a Cathedral Ceiling After a Four-Year-Old Re-Roof
A homeowner in a cold climate reports two-foot icicles at the eave and a water stain on the cathedral ceiling near an exterior wall. The roof is 6:12, covers 1,600 square feet, and was re-roofed four years ago with architectural asphalt shingles. Snow depth is about 8 inches. The attic is a cathedral assembly with 2x10 rafters, fiberglass batts, and a ridge vent; the inspector finds the soffit vents blocked by insulation and a bathroom exhaust fan terminating in the attic space. The ice barrier membrane visible at the eave extends only 18 inches up the roof slope. Gutters are present and functional. There are no roof leaks reported during summer rain, and the ceiling stain is dry at the time of inspection.
1. What factors most likely contribute to the ice dams and ceiling stain? Explain the heat and water path.
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The ice dams are probably being fed by warm attic air rather than by roof-material failure alone. Heat escaping through the cathedral assembly melts snow on the upper roof; the meltwater runs down to the colder eave, where it refreezes and forms an ice dam. Blocked soffit vents reduce cold-air intake, and the bathroom exhaust discharging into the attic adds warm, moist air. Once an ice dam forms, water can back up under the shingles. The ice barrier extends only 18 inches from the eave, which may not be far enough inland for this climate and snow load. The ceiling stain near the exterior wall is consistent with backup at the eave rather than a summer rain leak. The inspector should report these visible contributors and note that the exact leakage path and concealed moisture cannot be confirmed without further evaluation.
2. What should the inspector recommend, and what should not be attributed to the roofing material alone?
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The inspector should recommend correcting attic air leakage, improving insulation, establishing proper intake and exhaust ventilation, and terminating the bathroom exhaust outdoors. The narrow ice-barrier membrane should be noted and considered for correction at the next re-roof, but the inspector should not say that new shingles alone will solve the problem. The ice dams should not be attributed solely to defective asphalt shingles or to the gutters; they are strongly linked to heat loss and ventilation. The report should recommend evaluation by a qualified roofing contractor and an insulation or energy specialist, and it should state that snow cover limited the inspection of flashings and roof surface details.